1. Field of the Invention
This invention relates generally to memory systems and more particularly to First In First Out bipolar semiconductor memory systems which are especially useful as a buffer type memory in an electronic system application.
2. Description of the Prior Art
In the past, semiconductor memory systems have been developed which generally fall into two basic categories, namely dynamic memories and static memories. Dynamic semiconductor memories are made of either bipolar or MOS type components, and are characterized by the need to periodically refresh charge on various portions of the memory circuit in order to maintain a stored information state. On the other hand, semiconductor static memories are made of bipolar or MOS type components which are constantly connected to an energy source so that there is no need to refresh the memory circuits.
The static and dynamic memory systems in general are used as a memory storage function wherein information, during one period of time, is written into the memory system and the stored information, during another period of time, is subsequently read out of the memory system. One major disadvantage with this type of memory system operation is that it does not permit information to be written into the memory system at the same time that information is read out of the memory system.
Memory system designers have been particularly interested in recent times in developing memory systems that could function substantially as a First In First Out memory unit wherein data that is entered into the memory system will be sequentally passed through the memory system. One additional advantage of a FIFO memory system over a conventional sequential memory system is that data can be entered into the memory system at various speeds while at the same time data can be taken out of the memory system at the same or different speeds. The data or information that is first entered into a FIFO type memory system will be the first available data for output from the system. This has previously been done using fairly sophisticated software techniques and more recently, has been implemented in hardware using MOS type components. However, MOS implementation of a FIFO memory system is substantially slow.
Accordingly, a need existed to develop a high speed bipolar First In First Out semiconductor memory system which could be operated at speeds that are many times the speed of existing MOS FIFO memory systems.